As shown in FIG. 8, a hub unit system equipped with a hub ring 101 and an outer ring 103 is known as a bearing device for a wheel (Patent Document 1 and Patent Document 2). This bearing device for a wheel is equipped with the hub ring 101, an inner ring 102 fitted onto the hub ring 101, the outer ring 103 arranged in the outer periphery of the hub ring 101 and the inner ring 102, tapered rollers 104a and 104b respectively arranged between the outer ring 103 and the hub ring 101 and between the outer ring 103 and the inner ring 102, and retainers 106a and 106b having pockets retaining the tapered rollers 104a and 104b, respectively.
The outer ring 103 has an outer race 107 on the outboard side and an outer race 108 on the inboard side, and the hub ring 101 has an inner race 109 opposed to the outer race 107 on the outboard side of the outer ring 103 and a small diameter portion 110 with which the inner ring 102 is fit-engaged. Further, the inner ring 102 has on the outer peripheral surface thereof an inner race 113 opposed to the outer race 108 on the inboard side of the outer ring 103.
Generally speaking, a bearing device for a wheel of this type is assembled as follows. First, as shown in FIG. 10, the tapered rollers 104a and the retainer 106a on the outboard side are incorporated into the outer ring 103, thus effecting transition from the state of FIG. 9 to that of FIG. 10. After that, a seal member 112a is assembled to the outboard side of the outer ring 103.
Next, as shown in FIG. 11, the hub ring 101 is incorporated into the inner side of the outer ring 103, to which the tapered rollers 104a, the retainer 106a, and the seal member 112a have been assembled. After that, the tapered rollers 104b and the retainer 106b on the inboard side formed into an assembly 111b beforehand (hereinafter, this assembly will be referred to as the “roller assembly”) are assembled to the inner ring 102, which has the inner race 113 on the outer peripheral surface thereof, and the resultant assembly is externally fitted to the small diameter portion 110 before the seal member 112b is assembled. After that, an inboard side end portion 114 of the outer ring 103 is swaged from the outer side, whereby, as shown in FIG. 8, the inner ring 102 is held between a step portion 115 of the hub ring 101 and a swaged portion 116 of the hub ring 101.    (Patent Document 1) JP 11-44322 A    (Patent Document 2) DE 20209017 U1